I am trying to figure out the initialization process of VASP, and I found an INCAR tag NELMDL, on the wiki page of NELMDL, it is said that VASP requires 5-10 steps to obtain the reasonable orbitals. This seems strange, when setting ISTART=0 and INIWAV=1, the initial charge density is calculated by taking the superposition of atomic charge densities. So I could get reasonable charge density directly, and use it to calculate the reasonable orbitals by just one step.

My question is:

Why does it take 5-10 electronic steps to obtain reasonable orbitals?

Default: NELMDL

= -5 if ISTART=0, INIWAV=1, and IALGO=8

= -12 if ISTART=0, INIWAV=1, and IALGO=48

Description: NELMDL specifies the number of non-selfconsistent steps at the beginning.

If the orbitals are initialized using a random number generator (the

default in VASP), the initial orbitals are usually unreasonable and

the iterative matrix diagonalization willrequire 5-10 stepsto obtain

reasonable orbitals.The charge density corresponding to the initialIt is hence advisable to perform a

orbitals is also, at best, erratic.

few electronic steps while keeping the initial Hamiltonian fixed. This

initial Hamiltonian is usually determined from a superposition of

atomic charge densities.

Here are the Schematic representation of the self-consistent loop for the solution of Kohnâ€“Sham equations. I think it would only take just finishing this loop(Electronic steps) one time to get reasonable orbitals.